1. Field of the Invention
This invention relates in general to a data transceiver and method therein, and more particularly to an activation method in a data transceiver.
2. Description of Related Art
An adaptive equalization method is often used in a data transceiver to compensate for the amplitude and phase distortions introduced by a transmission channel. Generally, an equalizer is a discrete time filter for compensating amplitude and phase distortions. A channel is a time-varying channel with a typically long time constant compared to the symbol period. The channel may be viewed as quasi-static, with a relatively constant impulse response. Equalizers are also used to recover timing so that the local receiver clock and the remote transmitter clock are synchronous. Usually, the local receiver clock and the remote transmitter clock are asynchronous. If the timing is not recovered, the transmitted signal can be lost or additional incorrect signals can be added. If the receiver clock is slower than the transmitter clock, after a long enough period of time, one sample of the received signal will be lost. On the other hand, if the local receiver clock is faster than the remote transmitter clock, after a long enough period of time, an extra sample of the receiver signal will be obtained. Equalizers have been implemented to recover received timing and data in many communication systems.
Further, the equalizers have to be adaptive to compensate continuously for non-idealities of the channel. A data transceiver often uses an adaptive algorithm to correct errors that occur in subsequent information bits. The adaptive algorithm is generally implemented by adaptive filters in the data transceiver.
However, when using an adaptive equalization in a data transceiver, a key requirement is to initially recover timing in the data transceiver. Depending on a transmission system, this can be difficult because severe distortions can occur to the received signals. When initially activating the system, the data transceiver is not yet trained (or adapted) to equalize the received signals.
Because of the various operating conditions of a data transceiver, adaptive algorithms are used to adapt to particular transmission line conditions. In particularly difficult loops (in terms of loop loss and distortion), activation of the system can be difficult and unreliable due to the adaptive filters. One particular problem is the recovering of the received timing.
FIG. 1 depicts a simplified typical data transceiver. The transceiver includes a plurality of adaptive filters: an echo canceller (EC), an automatic gain control (AGC), a feed forward equalizer (FFE), and a decision feedback equalizer (DFE). The echo canceller (EC) removes the transmit signals (TXDAT) from the received signals (RX). A transmitter filter (TX FILTER) shapes the transmit signal spectrum. A D/A converter converts the transient signal to analog signals (TX) to be transmitted. An A/D converter converts the received signals (RX) to a digital representation. The automatic gain control (AGC) optimizes the received signal level. The feed forward equalizer (FFE) whitens noise from the receive signals and removes pre-sample distortion of the received signals. The decision feedback equalizer (DFE) removes post-sample distortion from the received signals. A slicer recovers the received signals (RXDAT). Error signals at the slicer (error_signal) are generated to adapt all of the adaptive filters, AGC, FFE, EC, and DFE. When using such an adaptive equalization method as shown in FIG. 1, recovering received timing can be a problem because severe distortions can occur to the received signals. A xe2x80x9cbadxe2x80x9d pulse can be shown in FIG. 3B. A large post-sample distortion would create a large amount of inter symbol interference (ISI), making the system difficult to activate.
Therefore, there is a need for an improved adaptive equalization method in a data transceiver. There is a need for a method which makes a data transceiver easy to activate.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses an improved adaptive activation method which makes a data transceiver easy to activate. The present invention provides an easy and reliable activation method for an adaptive equalization in a data transceiver.
The present invention solves the above-described problems by pre-loading at least one of the adaptive filters in the data transceiver with a fixed set of coefficients and allowing the other adaptive filters to adapt. Accordingly, the transmission line is pre-equalized for some of the more difficult conditions, and the data transceiver is easily activated. After the initial activation, all of the adaptive filters are allowed to adapt. The present invention ensures a reliable and robust activation, and it also allows the data transceiver to adapt to various line and noise conditions such that good performance can be achieved.
The present invention provides an activation method for adaptive equalization of received signals in a data transceiver having at least one adaptive filter. In one embodiment, the activation method includes: pre-loading a fixed set of coefficients on at least one adaptive filter to partially equalize the received signals such that the data transceiver obtains initial activation; and adapting the pre-loaded adaptive filter to recover the received timing and/or data. The pre-loaded adaptive filter can be adapted immediately after the activation of the data transceiver, or after the activation and a period of time thereafter. The period of time can be for example a period for recovering the timing and/or data at the data transceiver.
The present invention also provides a method of adaptive equalizing received signals in a data transceiver having a plurality of adaptive filters. In one embodiment, the method includes: pre-loading a fixed set of coefficients on at least one of the adaptive filters; adapting at least one of the remaining adaptive filters to partially equalize the received signals such that the data transceiver obtains initial activation; and adapting all of adaptive filters including at least one pre-loaded adaptive filter to recover the received signals.
One aspect of the adaptive equalization method of the present invention is that the adapting of the pre-loaded adaptive filter is operated immediately after the initial activation of the data transceiver has been achieved.
Another aspect of the adaptive equalization method of the present invention is that the adapting of the pre-loaded adaptive filter is operated after the initial activation of the data transceiver and a period of time thereafter. The period of time is a period of time for recovering received timing and/or signals in the data transceiver.
The present invention further provides a data transceiver for adaptive equalizing received signals. In one embodiment, the data transceiver includes at least one adaptive filter for removing distortions of the received signals; and means for controllably adapting the adaptive filter such that the data transceiver is readily activated, such that the received timing and/or signals are recovered.
One aspect of the data transceiver of the present invention is that the adaptive means pre-loads at least one of the adaptive filter with a fixed set of coefficients to partially equalize the received signals such that the data transceiver is readily activated, and adapts the pre-loaded adaptive filter with adaptive signals. The adapting means allows the pre-loaded adaptive filter to adapt immediately after the data transceiver has been activated, or after the data transceiver has been activated and a period of time thereafter.
In another embodiment of the present invention, the data transceiver includes a plurality of adaptive filters for removing distortions of the received signals; and means for controllably adapting the plurality of adaptive filter such that the data transceiver is readily activated, such that the received timing and/or signals are recovered.
One aspect of the another embodiment of the data transceiver is that the adapting means allows the pre-loaded adaptive filter to adapt with the adaptive signals immediately after activation of the data transceiver has been achieved. Alternatively, the adapting means allows adaptation of at least one of the remaining adaptive filters immediately after the activation of the data transceiver, but allows adaptation of the pre-loaded adaptive filter only after activation of the data transceiver has been achieved and a period of time thereafter.
The present invention also provides a data transceiver for adaptive equalizing received signals with a pre-sample distortion and a post-sample distortion. In one embodiment of the present invention, the data transceiver includes: an echo canceller (EC) for removing transmit signals from the received signals; an automatic gain control (AGC) for optimizing a gain level of the received signals; a feed forward equalizer (FFE), coupled to the automatic gain control (AGC), for whitening noise from the received signals and removing the pre-sample distortion; a slicer, coupled to the feed forward equalizer (FFE), for recovering the received signals; a decision feedback equalizer (DFE), coupled between the slicer and the feed forward equalizer (FFE), for providing feedback signals to the slicer to remove the post-sample distortion; and means for controllably adapting the FFE, EC, AGC, and DFE such that the data transceiver is readily activated, and the received signals are recovered.
One aspect of the present invention is that the adapting means includes an error generator, coupled between input and output of the slicer, for generating error signals. The adapting means pre-loads the FFE with a fixed set of coefficients and adapts at least one of the EC, AGC, and DFE with the error signals to partially equalize the received signals such that the data transceiver is readily activated. The adapting means allows the FFE to adapt with the error signals after the data transceiver has been activated.
Another aspect of the data transceiver of the present invention is that the adapting means allows the FFE to adapt with the error signals immediately after activation of the data transceiver has been achieved. Alternatively, the adapting means allows the FFE to adapt with the error signals after activation of the data transceiver has been achieved and a period of time thereafter.
One advantage of the present inventions is that they ensure a reliable and robust activation. Further, the present inventions allow the data transceiver to adapt to various transmission line and noise conditions in recovering the received data such that good performance can be achieved.